UHVDC Transmission Lines Research Articles

Calculation and Analysis of Electromagnetic Environment Indexes and Influence Factors of ±1100 kV UHVDC Transmission Lines

In order to study the influence of electromagnetic environment of ±1100 kV Changji-Guquan the UHVDC lines, the ground total electric field and ion current density of the HVDC line is studied in this paper by using the charge simulation method and Deutsch’s hypothesis-based analytical method. And the correctness of the method is verified by the measured results. The EPRI formula and CISPR formula are applied to study the audible noise and radio interference. At last, the influence of UHVDC transmission line parameters on the electromagnetic environment is analyzed, and the influence factors that restrict the construction of the UHVDC transmission lines are also studied. The results show that the minimum height of the pole is limited by the total electric field strength, and the influence of the roughness coefficient should also be taken into account when calculating the minimum height of the wire, while the selection of the diameter of the wire is constrained by both the ground total electric field and the audible noise.

Calculation Of Ion Flow Field In HVDC Transmission Lines Under The Influence Of Haze

Because of the influence of haze on the electromagnetic environment of HVDC transmission lines, this paper proposes a method for calculating the ion flow field considering the influence of haze based on the flux line method, and takes the Yunguang 800kV UHVDC transmission line as an example. A synthetic field intensity and ion flow calculation model with different haze and haze levels was established, and the resultant field strength and ion flux density under different haze conditions were obtained. The results showed that the ground synthetic field intensity and ion flux density under haze weather increased relative to normal weather, and increased with the increasing degree of haze weather pollution. This calculation method has reference value for the analysis of haze weather and corona impact factors in the planning and design of HVDC transmission lines.

Lightning Faults Analysis and Protection Measures for UHV DC Transmission Line

Lightning Faults Analysis and Protection Measures for UHV DC Transmission Line

Analysis of self-correlation characteristics of corona current spectrum on UHVDC transmission line

Analysis of the spectral characteristics of corona current is of great significance for optimizing the design of transmission lines. In this paper, a great number of corona current waveforms were measured on conductors in a large outdoor corona cage and actual UHVDC test transmission lines. First, a linear relationship with proportionality coefficient of approximately 1 between the spectrum components of corona current in the range of 5–20 kHz was found. Second, based on the similarity of the correlations between the spectrum components, a universal linear expression representing the correlation between the spectrum components of corona current under different conditions was obtained through data fitting. Finally, with the obtained expression, the spectrum components of the corona current at frequencies in the range of 5–20 kHz were estimated according to the spectrum component at 5 kHz, and then measured on the high altitude UHVDC test line segment located in Tibet, China. By comparing the estimated values with the measured ones, the validity and accuracy of the self-correlation expression between spectrum components was verified.

Contamination Deposited Characteristics of Polymeric Insulator on ±800 kV Chu-Sui UHVDC transmission lines

Contamination Deposited Characteristics of Polymeric Insulator on ±800 kV Chu-Sui UHVDC transmission lines

Study on the difference of chemical composition of insulator contamination on UHV‐AC and ‐DC transmission lines

For the ultra high voltage (UHV)-DC and UHV-AC transmission lines, their contamination characteristics are different. Thus, researching the contamination polluted degree of UHV-AC and UHV-DC lines by geoaccumulation index and enrichment factor method is an ingenious method. This study analyses and compares the chemical composition of contamination on parallel energised UHV-DC (800 kV) and UHV-AC (1000 kV) overhead transmission lines. The results indicate that the major cations of insulator contamination are Ca2+ , and NH4 +, and the major anions of insulator contamination are SO4 2− and NO3 − both on UHV-DC and UHV-AC lines. For the UHV-DC line, the concentrations of the same cations on the insulator bottom surface are higher than that of on the top surface. However, on the UHV-AC line, the same cation concentrations on the bottom surface close to the one on the top surface. The metallic elements of Ca2+ and Zn2+ are in seriously polluted degree. Also, the polluted degree of contamination on UHV-DC insulator is more serious than UHV-AC insulator. This study considers that field charging plays an important role in accumulating contamination.

Research on electric field distribution of UHVDC transmission lines and body surface during live working

Electric field distortion emerges around personnel working on live Ultra High Voltage Direct Current UHVDC transmission lines, especially when they move from ground-potential to equipotential positions. Unreliable protection threatens the safety of both workers and transmission lines. The current study investigates the electric field distribution of body surface during live working under transmission lines. To provide safety advice, live working person and tower models were established. The body surface field was calculated in different positions under ±800 kV transmission lines, and the distribution of the electric field was summarized.

Identification of Lightning Strike on ±800kV UHVDC Transmission Line Based on the PSCAD

This paper proposed an effective method of lightning stroke recognition. The characteristic of non-faulty lightning is that the correlation degree with the axis voltage approaches 1.This feature can identify lightning interference. The characteristic of the lightning failure is that when the flashover occurs, a large number of high frequency components in the lightning wave are immediately reduced; the characteristic of the ground fault is that contain less high frequency components. After wavelet transform, the ratio of high-frequency components caused by lightning stroke to middle and low frequencies components is larger than that of ground fault. This feature can be used to identify lightning fault and ground fault. This paper is based on the model of ±800kV UHVDC power transmission project from Yunnan to Guangdong, and simulation results show that the proposed method is effective.

Commutation Failure Influence on Power Converse in UHVDC Power System

For UHVDC transmission systems, the commutation failure of the DC system may cause the AC side power converse and may further lead to the AC line protection misoperation. This paper has analyzed power converse of AC system caused by commutation failure of DC system, and establishes the transmission line of UHVDC transmission line by using PSCAD/EMTDC simulation software. Using this simulation model to analyze how transition resistance in fault impact on power converse. The simulation results show: With the transition resistance increases, power converse presented a V shape change. By reducing positive sensitivity of sudden change relay or set a certain delay time (usually 40 ms) to start blocking mode pilot protection can prevent line protection misoperation caused by power converse.

Influence of wind speed and dust particle size on the corona characteristics of ± 1100 kV fitting models

At present, the UHVDC transmission lines in the Northwest China are inevitably built across sandstorm-prone areas, whereas the influences of strong wind and dust particles have not been paid enough attention in the existing design guidelines and standards. Since the corona characteristics are greatly influenced by environmental factors, to study the effect of sandstorm environment on the corona characteristics, corona tests were carried out on five ±1100 kV fitting models under different experimental conditions of wind speed and dust particle size in artificial sandstorm environment. The results show that the corona inception voltage decreases under the influence of wind and dust particles. Moreover, the voltage increases along with the wind speed rising, whereas the particle size shows little effect on the corona characteristics. Then the test results were verified and analyzed by electric field simulation and flow field simulation using ANSYS and Fluent software. These results could promote future DC corona mechanism study and practical engineering.

A Novel Traveling-Wave-Based Main Protection Scheme for $\pm $800 kV UHVDC Bipolar Transmission Lines

The UHVDC transmission system has been increasingly used because of the advantages in long distance and large capacity transmission. However, the existing traveling-wave-based protection for UHVDC transmission lines is not sensitive enough to properly detect the internal fault with high fault resistance. A novel traveling-wave-based protection scheme for bipolar UHVDC lines is proposed in this paper. The discriminative characteristic between the internal and external fault, embodied in the backward traveling wave, is extracted to formulate the main protection criterion. The faulty line is identified by the polarity of the voltage fault component. In addition, only the single-pole voltage and current of rectifier side are required for the proposed protection scheme. The simulation and field data tests show that the proposed protection scheme can make a correct identification of the fault section and selection of the faulty line in the $\pm $ 800 kV UHVDC system and $\pm $ 500 kV HVDC system. Besides, the proposed protection can correctly detect the grounding fault with fault resistance up to 500 $\Omega $ .

Corrosion mechanism and process of hardware of disc suspension type Insulators on ±800 kV transmission lines

Hardware corrosion on porcelain and glass insulators has occurred on ±800 kV UHVDC transmission lines in China. Iron cap corroded insulators all located at the negative polarity and pin corroded insulators concentrated in positive polarity. The corrosion mechanism is analyzed from the aspect of electrochemistry and the corrosion process is researched by means of spray water simulation tests. Mechanical and electrical characteristics tests and simulation calculation have been done. Test and calculation results indicate that iron cap corrosion can aggravate the contamination accumulation on insulator�s surface and decrease the flashover voltage. Pin corrosion can decrease the mechanical strength of insulators. XP-4C type porcelain insulator and electrolytic cell are used to research the influence factors of corrosion rate of hardware. The test results show that the contamination degree on insulators' surface and its component have considerable influence on the corrosion rate. The more serious the degree of contamination is, the faster the corrosion rate is. The sequence of cation that lead to the corrosion rate from fast to slow is K+>Na+>Ca2+>Mg2+, the sequence for anion is Cl->SO42->NO3-.

Influence of pin corrosion on mechanical characteristic of UHVDC disc suspension insulators and solutions

Hardware corrosion has occurred upon lots of suspension-type porcelain and glass insulators of ±800 kV Chusui and Xiangshang UHVDC transmission lines in China since October 2011. The cause of pin corrosion and its influence on the mechanical property of insulators are researched in this paper. The mechanical load that insulator bears under the circumstance of conductor icing and galloping is calculated by means of ANSYS software. Also, the failure forms of insulators under large mechanical load condition are analyzed. On the basis of this, the method that installing organic material sleeve onto the zinc sleeve to vary its corrosion area is proposed. The problem of mechanical strength decreasing of the insulators caused by expansion of corroded by-products is solved. Insulator samples with organic material sleeves of three structures including zinc sleeve half package type, flush type, and whole package type are made, and pin electrolytic corrosion simulation tests are carried out upon the three kinds of samples respectively by means of the spray water method. It turns out that half package type organic material sleeve alters the corrosion part of zinc sleeve effectively and the pins of insulators with two other kinds of organic material sleeves were corroded seriously. The electric field intensity of insulators is calculated by means of ANSOFT software. Calculation results indicate that the semi-conductive rubber sleeve provides the insulator with better electric field intensity characteristic.

Study on the Influence of Space Charge on the Upward Leader Emerging From the Conductors of UHVDC Transmission Lines

The space charge produced by the glow corona from tall objects is known to inhibit the initiation of upward leaders. However, in contrast to consideration of the glow corona at the surface of conductors caused by thunderclouds, the inhibitive effect of ion flow on the initiation of upward leaders from conductors due to dc operation voltage has been relatively neglected in previous studies of the leader progression model. In this paper, the glow corona at the surface of a conductor due to the thundercloud and the operation voltage have been analyzed quantitatively and compared with each other. It is found that the influence of the operation voltage on the distribution of ion flow is the largest in the area near the conductor. Since the operation voltage has a greater influence on the inception of the upward leader than the thundercloud, it should therefore also be considered in the leader progression model. A new simplified model is hence proposed to account for the distribution of ion flow under thundercloud conditions. In addition, a simulation experiment is designed to study the influence of ion flow on the initiation of the upward leader from a 6-bundled conductor, and the results are used to verify the validity of the simplified model. Finally, the model is applied to assess the influence of ion flow on the inception of upward leaders under different lightning currents. The calculation results show that the ion flow causes the upward leader to incept later, and reveal that the influence of the thundercloud on the inception of the upward leader is small, although it influences the distribution of the ion flow significantly.

Suppression method for electrolytic corrosion of porcelain insulators' iron caps on UHVDC transmission lines

In recent years, the phenomenon of electrolytic corrosion on porcelain insulators' iron caps has occurred in many HVDC transmission lines in China such as the Yunguang, Xiangshang, Tianguang, Gaozhao and Xingan HVDC lines. The validity of using U-shaped zinc rings to restrain iron caps' electrolytic corrosion is tested and verified in this paper. In order to research the influence of U-shaped zinc rings on the electric field intensity of insulators, Finite Element Method (FEM) simulation software was used to calculate the surface electric field of insulators with and without a zinc ring. The influence of zinc ring size on the inhibitory effect was studied by accelerated electrolytic corrosion tests, and the reason that zinc rings of the same size exert different inhibitory effects on insulators of different tonnage is explained in terms of iron caps' curvature radii and water pocket characteristics. Test results indicate that the installation of U-shaped zinc rings is useful to suppress iron caps' electrolytic corrosion, and that the inhibitory effect of zinc rings of the same size on insulators with larger cap curvature radii is better than that on smaller ones. Optimal designs of the structure and size of the U-shaped zinc ring and its service life are proposed in this paper, based on the test results and the actual engineering practice.

Simulation Study on Iron-Core Loss of Saturable Reactor at Rectifier Valve Side in HVDC Transmission Line

A PSCAD based 12-pulse converter model for HVDC power transmission, in which the thyristor model with reverse recovery characteristics and the model of nonlinear saturable reactor composed of nonlinear resistance model and controlled current source are contained, is built to research the influences of the transmitted DC current on the iron-core loss of the saturable reactor. Taking the A5000 converter valve used in the rectifier side of ±800 kV/4 750 A UHVDC transmission project from Jinping to Sunan as the example, the iron-core losses of the saturable reactor under three different operation conditions of the UHVDC transmission line are simulated, and the simulation results conform to the on-side measured data. The iron-core loss of the saturable reactor not only comes into being while the converter valve is switching on, but also during the switching off and the off-state of the converter valve. The iron-core loss of the saturable reactor increases with the rise of the DC current.

The UHVDC Transmission Line Lightning Disturbance Identification Based on the Morphology

Research and identify overhead transmission lines’ transient characteristic which was caused by lightning stroke is significant to develop the protection and improving its reliability based on transient state. A complex signal can be resolved into several parts which have respective physical meanings by mathematical morphology’s multi-scale decomposition and this can reveal the local features of waves. Therefore, the transient current of ±800 kV UHVDC transmission lines, caused by the non-fault lightning stroke, fault lightning stroke and other line short circuit, can be decomposed by the multi-scale morphology decomposition to extract the spectral energy from the high and the low frequency bands, and the ratio of those two spectrum energy forms main criterion to realize the identification between lightening disturbance and the fault states. According to the ratio of the maximum of the current’s amplitudes of decomposition waveform of the first head of current’s second scale and sixth scale, to further distinguish the lightning stroke fault from the line short circuit. Extensive simulations show that the approach is correct and effective.

A Earth Fault Section Identification Method Based on ANN

The method to discriminate the fault within or beyond the protective zone according to the signals with high frequency detected in protection has problem with low reliability when the resistance of earth fault is high. The transient voltage with low frequency detected in protection can reflect the size of fault intensity approximately, and the transient voltage with high frequency detected in protection in internal fault is bigger than that in external fault when the size of fault intensity is same. The high frequency transient voltage and low frequency transient voltage detected in protection are chosen as inputs and fault section as outputs for training and testing the neural network for fault identification in the UHVDC transmission line, fault section can be identified when input fault characteristic data to the trained model. A variety of transmission line earth fault situation are simulated by PSCAD, and this earth fault section identification method based ANN shows satisfactory performance, even the fault resistance is high.

Modeling of an ionized electric field on the building near the UHVDC transmission line

In this paper, a 3D upstream finite element method is developed to analyze the ionized electric field around the UHVDC transmission lines including the building near it. The ionized electric field around the building is reduced due to the shielding effect of the building and the shielding distance is about three times its height. The ionized electric field including the human body model on the building and away from the building is also taken into account. The ionized electric field distortion ratio of the human body model is discussed in this paper. The distortion ratios for the positions on the building are less than those on the ground.

Wind-Induced Response of UHV Guyed Single-Mast Transmission Tower-Line System

Ultra-high voltage guyed tower is typical structure of tall and slender, with the character of nonlinear and more sensitive to wind loads. Wind load is one of the most important control loads during design phase. A single-mast guyed tower recommended by a UHV DC transmission line was set as an example in this paper. The finite-element model of transmission tower-line system was built, based on Davenport, fluctuating wind velocity time-history was simulated, the result of wind-induced response was analyzed. The result indicates that, as for displacements of the nodes on guyed tower, the mean values of wind-induced response are greater than the displacements under the static equivalent wind loads. As for axial forces of the leg members on guyed tower, the axial forces under the static equivalent wind loads are less than the max values of wind-induced response.